The present invention relates to a cooperative operation method, a mobile communication terminal thereof, a mail transceiving method, and a communication system. More particularly, the present invention relates to a cooperative operation method between a basic processing part and an application in the mobile communication terminal comprising the basic processing part to manage a predetermined resource, the mobile communication terminal which uses the cooperative operation method, the mail transceiving method which is used in the mobile communication terminal, and a communication system capable of using the mail transceiving method.